1. Field of the Invention
The present invention relates to stage apparatuses and charged particle radiation apparatuses, and more specifically, to a stage apparatus having a braking mechanism and a charged particle radiation apparatus equipped with the stage apparatus.
2. Description of the Related Art
With scaling down of semiconductor elements, electron microscopes that measure and inspect semiconductor devices with greater precision have been increasingly demanded. In an electron microscope, a sample to be measured or inspected, such as a semiconductor wafer, is placed on a sample stage that is movable in, for example, X and Y directions (in directions perpendicular to the optical axis of an electron beam). Then, movement of the sample stage is controlled such that measured or inspected part of the sample is aligned with the irradiation spot of the electron beam.
JP 2009-259534 A discloses a braking mechanism for use in stopping a sample stage. More specifically, this document describes a technique for controlling an occurrence of servo vibrations after the sample stage has stopped. In this technique, after the sample stage has been positioned, current control performed by a current amplifier or a position control system that may cause servo vibrations is turned off. This causes the sample stage to be stopped with good stability. Furthermore, the braking mechanism is installed in order to suppress the sample stage from being drifted and thus displaced away from a target location and to ensure stiffness against disturbance. With this technique, vibrations and displacement of the sample stage which are caused by stopping of the sample stage is suppressed.
JP 2011-013825 A describes a technique for controlling an occurrence of residual vibrations after a stage has been positioned. More specifically, this document describes a technique for stopping a stage with a brake. In this technique, two piezo elements that are disposed opposite each other on a movable stage are pressed against a brake rail, thus stopping the stage. After the stage has been positioned and stopped, a current amplifier is turned off. This technique stiffens the stage against disturbance and noise that may affect the stage mechanism and can stop the stage with great precision.